1. Field of the Invention
The present invention relates to a valve apparatus for a muffler (or a noise silencer) which is interposed in an exhaust system mainly of an internal combustion engine of a motor vehicle. It relates, in particular, to a valve apparatus which opens a bypass passage for exhaust gases inside the muffler when an exhaust gas pressure inside the muffler has risen to a predetermined pressure.
2. Description of the Related Art
The applicant of the present application has earlier proposed the following valve apparatus for a muffler in Japanese Patent Application No. 110580/1998. Namely, the valve apparatus is provided with a housing which has a valve opening through which the exhaust gases pass, and a valve which opens and closes the valve opening. The valve is constituted by a plate valve which is capable of elastic deformation by deflection (or flexure) and one end portion of which is fixed to the housing. A valve seat is provided in the periphery of the valve opening on that surface of the housing to which the plate valve is fixed. The plate valve is caused to be seated on the valve seat in a state of being urged in a closing direction (i.e., a direction in which the plate valve is closed) by the elastic restoring force due to its own deformation by deflection. When an exhaust gas pressure exceeding this elastic restoring force is operated on the plate valve, the plate valve is deflected in an opening direction (i.e., a direction in which the plate valve is opened), whereby the valve opening is opened to passage.
However, the above-described apparatus has the following disadvantages. Namely, when the plate valve returns in the closing direction by the elastic restoring force when the exhaust gas pressure has decreased, the plate valve strikes the valve seat, resulting in consequent striking noises as well as wear on both the plate valve and the valve seat.
The present invention has an object of providing a valve apparatus for a muffler in which the above-described disadvantages has been resolved.